The invention relates to a utility monitor for detecting and storing power line disturbances and, more particularly, to a utility monitor having a built-in differential between over-voltage triggering and resetting and under-voltage triggering and resetting and providing storage of a preselected number of cycles of said input sinewave voltage before and after the detected power line disturbance.
In data processing systems the machines often require checking because of some detected problem. Very often there is no obvious cause of the problem and the service man logs the call in as no-trouble-found. In many cases the utility line is suspect. Accordingly, the cause of machine problems can be traced by detecting line dips or over-voltages and storing the waveshape before and after the fact, thereby, retaining valuable diagnostic information.
A problem with high gain sensors as used in utility monitors is that they respond erratically to the fluctuation of voltages being sensed at the threshold switching point. This has become known as the threshold switching indecision. This problem has been solved in prior utility monitors by using a small amount of positive feedback around an operational amplifier, which is utilized to do the comparison between the voltage being monitored and the threshold, to introduce an offset or differential between the setting and resetting thresholds. This threshold setting and resetting differential or hysteresis, as it is called, is practical for only relatively small differentials and is not always suitable where a large set-reset differential and a variable reference are desired.
When utility monitors are used to monitor voltages of quite different values, the threshold setting must be changed accordingly. This has been previously accomplished by providing a rotary switch arrangement which is capable of selecting a number of threshold levels for operation of the utility monitor with specific voltage level inputs. Of course, a large number of threshold settings require an equally large number of rotary switch positions.
The prior art utility monitors have, in some cases, just kept track of the interrupt within a counter and subsequently compared their time of occurrence with the time of occurrence of the machine problem to determine if the problem was a utility line problem or an actual machine fault. Where it is desired to do more than just capture utility interrupts within a count, display arrangements have been provided, such as cathode ray tubes, where photographs are taken of the scope which includes the waveform before and after the interrupt. Of course, more elaborate schemes such as tape recording outputs have been provided to obtain a trace of the voltage fluctuation before and after the interrupt. These arrangements are expensive and do not lend themselves to a simple built-in utility monitor in a data processing system.